Gleissberg cycle of solar activity

We propose extending the solar activity cycle back to year 1500 in order to study the Gleissberg Cycle. The Sunspot Index Data Center data can be extended using aurora records for the period from 1500 to 1700. We chose Kuklin's method of extension as it has the highest probability of fitting reality. Hoyt & Schatten's critical analysis of the standard sunspot cycle brought out some differences with SIDC data from before 1900. These authors proposed a solar cycle going from 1610 to the present. Starting from these two versions of activity cycles (Fig. 1), we construct two versions of the Gleissberg cycle (Fig. 3).